[karaterobot]

It's because they're designing it in Figma or Sketch, and of course infinite scrolling doesn't work in Figma and Sketch. If you don't predict this problem intuitively, you won't catch it until it's been implemented.

Ideally, there is a QA pass on staging, involving the designer, in which more than "does this feature work as written in the ticket" is the question you try to answer before releasing the feature. Many teams don't do this, and the blame for that lies with different people in different organizations I've worked in.

But developers often sneeringly deride designers for not catching things like this — "you had one job, lol" — but the sad truth is that there's no testing suite to help designers catch stupid mistakes. Speaking practically, the unit tester for a design is often the developer who tries to build it. Imagine what your interpreter or compiler or testing framework would say about your intelligence if it could talk!